. The best way to use firearm armies is to incorporate them with pikes. Normally you should have 2 pikeman units for every 1 firearm unit. Some cavalry is needed if the enemy has other range units. If the faction has no pikemen, spearmen or hvy infantry works fine too though they are more susceptible to cavalry charges.

. Fireams units should be deployed in 2 deep rows to maximize their firing rate.

. Deploy firearm units in the front of pikemen at the start and only move them back behind the spear wall when enemies close in. Put your gunners in f.a.w off and micro them to snipe any the units who are not engaged yet or better yet, snipe the enemy general.

. Never engage your gunners in melee, even if their defense and melee are good, they will still sustain heavy casualties. Use cavalry to take out flankers and retreat your gunners or better yet, place pikemen on your flanks and rear to form a box.

. Hope this helps.